Apparatus for manufacturing electric resistor



J1me 1965 P. w. KOUMANS ETAL 90,043

APPARATUS FOR MANUFACTURING ELECTRIC RESISTOR Filed Sept. 13, 1963 4Sheets-Sheet 1 INVENTOR.

PETRUS W. KOUMANS HENRICUS I? STAL June 22, 1965 P, w. KOUMANS ETAL3,190,043

4 Sheets-Sheet 2 FIG.3

INVENTOR PETRUS W KOUMANS HENRICUS F. STAL BY APPARATUS FORMANUFACTURING ELECTRIC RESISTOR 4 Sheets-Sheet 3 Filed Sept. 15, 1963FIG.4

FIG.6

INVENTOR. PETRU S W. KOUMANS S$NRICUS R STAL J1me 1965 P. w. KOUMANSETAL 3,190,043

APPARATUS FOR MANUFACTUR ING ELECTRI C RES I S TOR Filed Sept. 15, 19634 Sheets-Sheet 4 IN VEN TOR. PETRUS W. KOU MANS HENRICUS R STAL BYUnited States Patent 0 3,190,043 APPARATU FUR MANUFACTURWG REdlSTtlitPetrus Willem Kournaus, Emmasingel, Eindhoven, and Henricus Petrus Stal,Eindhoven, Netherlands, assignors to North American Philips Company, lncNew Yorir, N.Y., a corporation of Delaware Filed Slept. 13, 1%3, Ser.No. 368,805 7 Claims. (Cl. 51-67) The invention relates to apparatus formanufacturing resistors with a predetermined resistance value. Saidapparatus is provided with means for rotating the resistors while heldat their ends, and with at least one rotating grinding disc which isdisplaceable parallel to itself in a manner such that the grinding discis capable of cutting a helical groove with a given pitch in a layerprovided on electricallydnsulating material of the resistor body.

In known apparatus the grinding disc, during its parallel displacement,is held at right angles to the center line of the resistor. Since thisangular condition of the cutter does not bear any relation to the pitchangle of the helical groove to be ground, an unfavorably shaped grooveis obtained. Devices are also known in which the grinding disc isadjusted to a given angular position with respect to the center linethrough the resistor at which it is fixed for a given series ofresistors. In this case a groove having the same pitch is ground in allresistors, a favorable shape of the groove being obtained so long as theangle of the grinding disc corresponds to the pitch angle. However, theresistance value of ungrooved resistors i.e. the layer which is to begrooved to provide a given resistance value, varies for almost eachindividual resistor, even if they are pre-graded. Therefore, if thehelical groove for all resistors, through a given distance, is parallelto itself, and the groove length of all resistors is the same, theresistance values of the finished product will vary individually, andthe tolerance with respect to the desired value may be inadmissiblylarge. Also, if the displacement of the grinding disc is continued, i.e.the length of the groove is varied until the desired resistance value isobtained, the groove will not extend through an equal portion of thesurface in various resistors. For favorable heat distribution of aresistor operating in an electric circuit, this latter isdisadvantageous. In addition, if a groove is ground with a variablepitch, the fixed grinding disc will again not be in the most favorableangular position with respect to the resistor for a favorable grooveshape.

The object of the invention is to provide a device for manufacturingresistors, in which the above problems are avoided. For that purpose,according to the invention the shaft on which the grinding disc ismounted is swingably in a plane which extends parallel with the centerline of the holding means or longitudinal axis of the resistor. Meansare provided for adjusting the displacement of the grinding discparallel to itself and also for adjusting the angle which the grindingdisc makes with the center line through the holding means. These meansare mutually coupled in a manner such that for any value of adjustedpitch, the angle which the grinding disc makes with the center line ofthe holding means corresponds to the pitch angle. Therefore, for anyadjustment of the pitch for the groove to be ground in a resistor, thecutter will be at the correct pitch angle, as a result of which a sound,clean groove is obtained. The pitch is adjusted for each resistor havingthe same value so that the grooves are all the same length over equalparts of the surface of the resistor which is as favorable as possible.The correct adjustment of the cutter varies even if grooves are to beground with a variable pitch.

The adjusting members for the parallel displacement of the grinding discmay consist, for example, of a spindle Ziglhhfidd Fatented June 22, 1%65provided with screw-thread. in a preferred embodiment of the invention,the adjusting members, however, consist of two axially displaceablerods, the first of which is connected at one end to a stand which ismovable parallel to itself and which carries the grinding disc, whilethe second rod is connected at one end to a lever mechanism which causesthe grinding disc to swing when under the influence of a displaceableprofiled member engaged by the other end of each rod. The profiledmember may impart an axial displacement to the two rods, as a result ofwhich a coupled adjustment of the two members is obtained.

The profiled member may be constructed, for example, as a cup-shapeddisc. However, it is of advantage to use an embodiment in which the freeends of the rods cooperate with a plate, of which one side has thedesired profile, said plate being capable of rotating in its planearound a shaft at right angles to the plane in a manner such that theangle which the profiled side makes with the center line through theholding means ofthe resistor is varied. In addition, the plate ismovable parallel to itself and in a direction at right angles to thesaid centre line. In this embodiment a very simple coupling of the rodsis obtained which serves for the parallel displacement and for theangular movement of the grinding disc. The profiled side is turned tothe suitable position for obtaining the desired pitch and pitch angle.When the plate is displaced the grinding disc always corresponding tothe pitch angle. In this case, a favorable effect is obtained if thefree end of the rod is provided with a roller or stud located on theprofiled side, in which, in the starting position of the profiled plate,the axis of rotation of this plate and the center point of the stud orroller of that rod, which when being displaced axially causes themovement of the grinding disc parallel to itself, are in alignment. Thestud or roller of the second lever being located beside the first studor roller on the profiled side. In the starting positon of the plate thedesired angle adjustment of the grinding disc may be obtained withoutthe grinding disc moving parallel to itself.

In a further embodiment of the invention two separately driven grindingdiscs are provided which are influenced by two axially displaceablerods, the rods which ensure the parallel displacement of the grindingdiscs being each connected pivotably to one end of a lever and the rodswhich ensure the angle adjustment of the grinding disc being connectedto the ends of a second lever, said levers being rotatable around acommon shaft, the rods located at one side of the axis of rotation beingprovided with rollers or studs which cooperate with the profiled side ofthe plate. In this construction two grooves can be ground on theresistor which end at a short distance from one another. For the bestdissipation of heat of these resistors in an electric circuit this has afavorable elfect.

According to the invention, members may be provided for adjusting theangular position of the profiled side of the plate with respect to thecenter line through the holding means in accordance with the previouslymeasured resistance value of a resistor to be processed and the desiredfinal value of this resistor, and for holding the plate in its adjustedangular position. The resistance value of each of the resistors to beprovided with grooves may be measured while in the device, after whichthe desired angle adjustment of the profiled side of the plate is madewith reference to this measured result. Then the plate is held in thisposition, for example, by means of a magnet.

In a further embodiment according to the invention a rotatablecylindrical cage is provided, the end faces of which contain a number ofopposed chucks or clamping devices, which are at regular distances fromone another and lie in a circle with their center lines aligned. Eachclamping devices can be moved in an axial direction tocord 17 forconvenience.

arouses (.3 ward each other such that a resistor can be clamped at bothends therebetween, said clamping devices being electrically insulatedwith respect to the cage. This arrangement is excellently suitable formass production. One of the grinding discs may be located outside andthe other inside the cage.

In order that the invention may readily be carried into effect, it willnow be described more fully, by way of example, with reference to theaccompanying drawing, in which FIGURE 1 shows the diagrammaticillustration of the apparatus for grinding a helical groove into aresistor.

FIGURE 2 is a plan view of the device.

FIGURE 3 shows a structural detail of the profiled plate, the slidebeing in the starting position.

FIGURE 4 shows a detail taken on the line IV-IV in FIGURE 2.

FIGURE 5 shows part of the elevation in the direction of the arrow V inFIGURE 4.

FIGURE 6 shows a cross-sectional view taken on the line VI--VI in FIGURE4, in which a few component parts are not shown for reasons of clarity.

FIGURE 7 shows the cage with clamping device for the resistors, in whichalso the driving is shown.

FIGURE 8 shows an elevation of the driving disc in the direction of thearrow VIII in FIGURE 7, and

FIGURE 9 shows the various positions of the resistor in the cage.

In the principal diagram shown in FIGURE 1, a resistor to be processedis indicated by 1. The resistor which comprises a resistance layerprovided on electrically-insulating material, is clamped with its endsin a rotatable clamping member 2. A grinding disc 3 is connected to ashaft 4 which is driven by a motor 5. The grinding disc .is pivotablearound a point 6 in a plane parallel to the center line of the resistor.An axially movable rod 7 which can slide in bearings 8 and 9 ensures thedisplacement of the grinding disc required for the pitch of the groove.In addition, a lever 11) is provided on the motor 5, against which oneend of a second axially movable rod 11 is located. The rod 11 is capableof sliding in bearings 12 and 13. The bearings i5, 9, 12and 13 areprovided in a stand 14. In addition, a slide is provided which iscapable of sliding in bearings 15 and which is shown by a At one endthis cord is wound on the clamping member 2 with a few turns and can bedisplaced at its other end in the direction of the arrow by a drivingmeans (not shown). On the slide or cord 17 a rod 13 is connected bymeans of a hinge 19. The ends 20 and 21 of the rods '7 and 11 engage therod 18, the end 211 being in alignment with the center line of the hinge19 in the starting position. In addition, a cam stud 2.2 is providedwhich is rotatable around a shaft 16 connected in the stand 14 which camstud can be adjusted by means of a driving motor 23. An adjusting pin 24is provided between the cam stud 22 and the rod 18 is slidable in abearing 25. A spring 26 pulls the rod 18 against the adjusting pin 24.

The operation of the device above described is as follows:

Beforethe resistor 1 comes into position for grinding its value ismeasured in any suitable manner and the cam stud 22 is adjusted withreference to this value and the final value desired for the resistor tobe ground. The adjusting pin 24 is moved by the cam stud, which movementistransmitted to the rod 18 which rotates or pivots around the hinge 19to the desired position and is fixed in that position by any suitablemeans (not shown). As a result of the rotation of the rod 18, the rod 11is moved axially as a result of which the shaft of the grinding discswing around the pivot 6 through the lever 1t and the grinding disc ispositioned at an angle with the center line of the resistor. Thisangular position of the grinding disc exactly corresponds to the pitchangle of the groove 4ito be ground into the resistor, as a result ofwhich a favorable shape of the groove will be obtained. For eachresistor the rod 18 is adjusted by the cam stud at that value at which apitch is obtained of a size such that the groove extends over a portionof the resistor which is as favorable as possible. Now the slide or cord17 is moved in the direction of the arrows by known means (not shown)while the grinding disc rotates. The resistor is rotated around itscenter line, while the rod 18 is simultaneously moved to the left in thedrawing. Both the rod 7 and the rod 11 are moved axially, the axialdistance moved being dependent upon the angular position of the rod 18.The grinding disc is therefore moved parallel to itself or parallel tothe centerline of the resistor by the rod 7. A given pitch of the groovebeing obtained as a result of the rate of movement of the rod 7 and therotation which the resistor experiences. The angular position of thegrinding disc does not vary, since the rods 7 and 11 are of equallengths and are moved through the same distance by the rod 18.

It is not necessary for the rod 18 to be straight. If, for example, ithas a curved shape, the grinding disc, while grinding, will have anangular movement, while the axial displacement of the disc parallel toitself is also variable. Consequently, a groove will be ground with avariable pitch, the angular position of the grinding disc neverthelessbeing such that the disc has the correct pitch angle at any moment.

A machine will now be described with reference to FIGURES 2 and 6 whichoperates according to the principle of the diagrammatic appaartus shownin FIGURE 1 but in which two grinding discs are used, two grooves beingground on the resistor each extending over substantially one half of theresistor. A resistor 27 is held by clamping members 28 and 29 which areprovided in an electrically-insulated manner in a cage shown and described in connection with FIGURE 7. The clamps are capable of rotating.Two grinding discs 30 and 31 are each capable of cutting a groove on onehalf of the resistor 27 and are connected to shafts 32 and 33. Thedriving means for the shafts 32, 33 are indicated by 34. The drivingmeans 34 are each connected to sleeves 36 by means of bifurcated arms35. The sleeves 36 are each rotatable around its center line and aresupported on plates or stands 37 and connected to the stands 37 by meansof bearing braces 38. The bifurcated arm is connected to one end of eachsleeve by means of a screw 39 (FIG. 6). As best seen in FIG. 6 thesleeves comprises bearings 4d and 41 in which a shaft 42 can slide. Thisshaft is provided at one end with an arm 43 which is connected by meansof a pin 44 in a slot 45 of a supporting member 46 connected to thedriving means 34. When the shaft 42 moves the driving means 34 willswing around the pivot provided by bifurcated arm 35, the grinding discbeing made to engage or to disengage the resistor 27.

The stands 37 on which the sleeves 36 are supported are also providedwith braces 48 comprising bearings. Shafts 49 extend through thesehearings and are rigidly connected to supports 5% at each end. Thesesupports 5% are connected to a base plate 51 of the device. By thisassembly the stands 37 can be moved parallel to themselves, the bearingsof the braces 48 sliding on the shafts 49. The end of the shaft 42carries a block 53 which is provided with a slot. A pin 54 of a lever 55is located in the slot. This lever is pivotally supported by a pivotshaft 56 which is supported on the stand 37 by means of a brace 57.Attached to the other end of the lever 55 is a soft iron core 52 whichis attracted by an electro-magnet 73, the shaft 42 being thus moved orslid in the bearings 4d and 41. A spring 58 biases the lever 55 off themagnet. An adjustable stop member 5h prevents the lever from moving toofar.

As seen in FIGS. 4 and 5 each of the sleeves 36 also has an arm 60rigidly connected thereto. Attached to the end of the arm 6% is a pm 61to which an arm 62 is pivotally connected. Each arm 62 is connected to arod 63 and 64 respectively (FIG. 2). The rods 63, 64 are journalled sothat they can be moved or slide axially in supports 65 mounted on thebase plate 51. If the rods 63, 64 perform an axial movement, the arms 60and 62 cause the sleeve 36 to rotate around its center line, whichrotation is transmitted by the bifurcated arm 35 and thence to thegrinding disc which, as a result, is caused to swing in an angle withthe center line taken through the resistor.

Similarly rods 66, 67 are provided in a manner such that they. can bemoved axially in supports 65. These rods 66, 65"? are connected at oneend to the stand 37. When the rods -65 and 67 are moved axially, thegrinding discs 30 and Ell connected to the stand 37 are consequentlymoved parallekto themselves i.e. in planes parallel with thelongitudinal axis of the resistors. One pair of the rods 64 and 67 areprovided with adjusting rings 65a. Between these adjusting rings and anupright edge 68 of the support 65 springs 6Q, '70 are provided. The rods63, 64-, 66, 6'? have a thickened portion 71, 72 at one end which areslotted at '75, '74. A lever 75 is pivotally mounted on shaft '76mounted on the base plate 51. The ends of lever 75 are provided withpins I? which extends into the slots 73 of the rods 63, 54. A secondlever 7% spaced from lever T5 is also pivotally mounted on shaft '76 andis provided with pins till which extend into the slots 74 of rods 65 andd7. The rods 63 and 66 each have an extension member 823, 83, each ofwhich is provided with a roller 84 and 85. These rollers engage one side36 of a profiled or cam plate 87 as a result of the force of the springs69 and 7d acting through rods 64, 67 and levers i5, '79. in theembodiment shown, the side 86 of the plate has the shape of a straightline but may also have a different profile. The plate 37 is carried by aslide $8 which contains bearings 89 by which the slide is movable onshafts 96). These shafts are connected in supporting members 91, $2which are rigidly connected to the base plate 51. An arm S 3 is providedon the slide 38 and an arm 94 is provided on the plate 87 (PEG. 3).These two arms are pivotally connected by means of the shaft 95. Theprofiled plate 87 is thus rotatable around the shaft 95. The plate isfurther provided with a projection 96 to which a roller $7 is connected.If the slide rests against the support 92 the roller may engage arotatable cam $8 of which the driving means are not shown. The cam 3 isrotatable around the shaft 99 connected to the base plate. The profiledplate 87 can be held in the desired position with respect to the slide88 after rotation around the shaft 95 by means of an electromagnet 1th?(shown below plate 37) connected on slide 83. Pins ltill and 102 arealso provided on the slide 33. A cord M93 is connected to the pin 161which cord is wound around a drum 104 which is coupled to a motor res bymeans of a coupling 1%. A spring lltll is connected to the pin 1% whichspring is connected to a fixed point 108 of the base plate.

The operation of the device as illustrated in FIGS. 26. In the startingposition the slide 88 with the plate 87 is in the position in which theslide engages the supporting member hi2. In this case the roller 9'7presses against the cam 98 (shown in phantom) and the magnet we isswitched off. The grinding discs are at the starting positions of thegroove to be ground in the resistor and are swung outwards by means ofthe magnets is and associated linkage. The shaft of the roller 84 islocated on the center line of the hinge shaft 95 (see FIG. 3). When theresistor is introduced into the clamping members 2% and 29, theresistance valve of the layer to be provided with a groove is measured.Having this measured value and knowing the desired resistance value tobe ground, the cam 93 is turned to the desired position by any suitablemeans (not shown). The plate 8'7 (shown in its starting position in FIG.2') is therefore rotated around the shaft 95, however, the roller 84,being coaxial with shaft 535 in the starting position, is not moved byrotation of the plate about pivot 95, whereas the roller 85 is moved.This can also be seen in FIG. 1 where the head of arrow 2i? correspondswith roller 84 and rod 18 corresponds with plate 37. The rod s3 and therod 64 connected to roller 55 by the lever are consequently movedaxially whereby the rotating grinding discs 30, Si. are moved to thecorrect pitch angle through the linkage including the arms tit) and 62,sleeve 3d and bifurcated arm 35. When the magnets 73 are switched offthe circumference of the grinding disc comes into contact with theresistance layer by movement of the lever 55 and the shaft 42.Simultaneously the motor res becomes operative, in known manner, wherebythe plate 37 with the slide 83 are moved on guides 99. The rollers 84and are now displaced against the pressure of the springs so and 7t bythe side as of the plate and the stands 37 are moved parallel tothemselves by the axial movement of the rod 66 and the rod d7 coupledthereto by the lever "75 the desired pitch being thus cut on theresistor. In the embodiment shown in FIG- URE 2, in which the side 86 isstraight, the roller 85 which displaces the rods and d4 axially is notnecessarily moved during the parallel movement of the plate, so that theangular position of the grinding disc remains the same. When theresistor has been processed until the desired resistance value isreached, the motor 166 stops, the magnets '78 are energized, as a.result of which the grinding discs are swung away from the resistors,and a new resistor to be processed is put in its place. At the same timethe slide 83 and the plate 87 move to the starting position and themagnet 1% is deenergized as a result of which the plates 3%, 37 canagain be adjusted by the cam 98 to the correct position for processingthe following resistor.

Consequently, for each resistor processed an adjustment is made toprovide the correct pitch for the groove formed over a portion of theresistor which is as favorable as possible for minimizing rejects.

It is not necessary for the plate 87' to have the shape shown. The side86 against which the rollers 84 and 85 press, may also have othershapes, for example, convex or concave; the pitch of the groove on theresistor will then be varying.

FTGURES 7, 8 and 9 show the mechanism, which ensures the supply andadjustment of the resistor with respect to the grinding disc. Theresistors are supplied to a cage lid which is provided with fivepositions a, Z), c, d, and e for receiving a resistor. These positionsare provided by two rotatable circular discs 111, 112 the circumferenceof which is provided with gear teeth 113, 114. In these five positionsare opposed clamping members 2%, 29 of known telescopic construction andoperation. These members are mounted for movement in a direction atright angles to the discs ill, 112 in any suitable manner. The clampingmembers are electrically insulated with respect to the discs, as aresult of which it is possible to measure the resistance value of theresistor at any desired moment while held in the chucks or clampingmembers. Discs 111, 112 are connected to shafts ll? and 113 which areeach journalled into two supporting members H9 and 12%. A pinion 121which is connected to a shaft 122 cooperates with the teeth 113. At theother side of the shaft 122 a similar pinion 12.3 cooperates with theteeth 114. The discs 111 and 1112 are driven by the shaft 118 on which adriving mechanism is provided in the form of a plate 125 which isprovided with grooves 124. An arm 12 5 which can engage the grooves ofthe plate 125 is connected to a sleeve 127 which is connected, with ashaft 128, to a bearing 129 which is connected to the base plate The arm32% and the plate 125 operate in the manner of at Geneva wheel. Thesleeve 127 can rotate by means of the driving chain 133 and a sprocketwheel 131. In addition, two supporting members 132 are provided whichare connected to the base plate. In these supporting members a shaft 133is journalled which is provided with a toothed wheel 134 at both ends.These toothed wheels intermesh with the toothed wheels 135 to which theshafts 136 are rotatably connected, which shafts are each rotatable in abearing of the supporting members 132. When rotating, the two toothedwheels 135 will rotate equally rapidly. prise a coupling disc 137 towhich, for example, a friction disc 13% is provided. This disc may comeinto engagement with a disc 139 on the clamping members 28, 29. A leverMi) which is pivotal around a shaft 141 engages with one arm 14?. in agroove 143 on the shaft 136 and is connected with its other arm to a rod144. This rod is passed through the base plate and its end engages a camWheel 145 which is connected to a shaft 146 which is again coupled to asprocket wheel 147 with a chain 139.

' A resistor is supplied by means of a known chain conveyor 149 (FIGURE9) and is deposited in a suitably shaped member 150 so that it entersinto the space between the discs Ill and 112 of the cage. Then theclamping members 28 and 29 are closed by any suitable means (not shown).The chain 130 causes the arm :26 to rotate as a result of which theplate 125 is moved to a next position, in which the discs 139 of theclamping members remain closed by a guide (not shown) and the clampsconsequently remain holding the resistor. the position b the resistancevalue of the layer to be cut is determined. The measuring device (notshown) includes measuring pins 151, 152 which resiliently engage theinsulated clamping members 28 and 29. Knowing this value and the desiredvalue of the resistor to be ground, the required adjustment is made atthe cam stud $8, (FIGURE 2) which ensures adjustment of the profiledplate $7. In the condition 0 (FIGURE 9) the cams 145 force the couplingdiscs 137 against the discs 139 of the clamping device through the rod144 and the lever 140. Now a rotation is imparted to the resistor. Themotor for obtaining the rotating movement of the resistor is not shown.This may be coupled, for example to the driving means of the profiledplate i.e. elements 194-166. The grinding discs 30, 31 cut a helicalgroove with a given pitch into the resistor body in the manner alreadydescribed. The measuring pins 151, 152 during grinding measure the valueof the resistor. If this has reached the desired value, the magnets '78(FIGURE 2) are energized, the grinding discs being thus moved away fromthe resistor. Somewhat later the rods 144 on cam 145 move downwards andthe coupling 137 is opened. When turning to position a the discs 139 aredecoupled by an arm 155 which is partially shown in FIGURE 7 and theprocessed resistor is conducted away. In the position 2 the clampingmembers remain opened.

It maybe clear that an adjustment cage with five positions is notnecessary, although it has proved useful.

From the above it will be apparent that the device is suitable forgrinding resistors on which at least one groove is provided and in whichthe grinding disc is adjusted to the most favorable pitch for eachindividual resistor.

We claim:

1. Apparatus for manufacturing resistors ofpredetermined value having ahelical groove having a pitch angle comprising means for holding aresistor, means for rotating said resistor about its longitudinal axis,rotating cutter means, a first means for moving said cutter means in aplane parallel with the said axis of said resistor for cutting a helicalgroove in said resistor, a second means sup- The shafts 135 com- 3 a3porting said cutter means for movement to the pitch angle of saidhelical groove, and a meansv operatively connected with both said firstand second means for establishing the rate of movement of said cuttermeans as well as the angle of said cutter means.

2. Apparatus for manufacturing electric resistors having a predeterminedvalue comprising at least one clamping means for holding a resistor tobe processed, means for rotating said clamping means and said resistor,at least one grinding disc including means for driving said disc, at

least one slidable member mounting said grinding disc means for movementin a plane parallel with the longitudinal axis of said resistor, atleast one means mounting said disc means for angular movement relafiveto the longitudinal axis of said resistor, and adjustifig meansoperatively connected wtih said slidable member and said mounting meansfor angularly and slidably moving said disc whereby a helical groove iscut in said resistor and said disc is operated at the pitch angle ofsaid helical groove.

3. Apparatus according to claim 2 wherein said adjusting means comprisesat least two axially displaceable rods, one of said rods having one endconnected with said slidable member for moving said slidable member insaid plane, the other of said rods having one end connected with saidmounting means, and a movable member having a profiled surfaceoperatively connected with the other ends of each said rod forestablishing the said pitch angle of said groove and said cutting discand means for moving said profiled member in its starting position forselecting the pitch angle required. '4. Apparatus according to claim 3wherein said profiled member is rotatable about an axis perpendicular tosaid surface in its starting position whereby the angle defined by saidsurface and the centerline of said resistor is varied, means for holdingsaid profiled member in the selected position and means for linearlymoving said profiled member in a plane substantially normal to thecenterline of said resistor.

5. Apparatus according to claim 4 wherein the axis of rotation of saidprofiled member and the longitudinal axis of the rod for moving saidslidable member intersect in the starting position of said profiledmember.

6. Apparatus according to claim 3 wherein two separately driven grindingdisc means are provided to form helical grooves in a resistor body, twoslidable members mounting said grinding disc means, two means mountingsaid disc means for angular movement, two pair of rods connecting eachsaid slidable member and mounting means for angular movement of saidcutting discs, and a pair of levers interposed between said profiledmember and each of said two pairs of rods, one said lever connecting thecorresponding rod in each said pair with said profiled member and theother of said pair of levers connecting the remaining rods of said pairsof rods.

'7. Apparatus according to claim 2 with the adidtion of rotatable cagemeans supporting a plurality of said clamping means, said cage meanscomprising a plurality of axially movable clamping members, a pair ofrotatably mounted parallel spaced wheels supporting said clampingmembers evenly spread in a circular array, and means for driving saidclamping members in only one position thereof.

References Cited by the Examiner UNITED STATES PATENTS 1,660,468 2/28Bath 51-50 2,669,811 2/54 Henderson 5l37 2,884,746 5/59 Rus et al 51-37LESTER M. SWINGLE, Primary Examiner.

I. SPENCER OVERHOLSER, Examiner.

1. APPARATUS FOR MANUFACTURING RESISTORS OF PREDETERMINED VALUE HAVING AHELICAL GROOVE HAVING A PITCH ANGLE COMPRISING MEANS FOR HOLDING ARESISTOR, MEANS FOR ROTATING SAID RESISTOR ABOUT ITS LONGITUDINAL AXIS,ROTATING CUTTER MEANS, A FIRST MEANS FOR MOVING SAID CUTTER MEANS IN APLANE PARALLEL WITH THE SAID AXIS OF SAID RESISTOR FOR CUTTING A HELICALGROOVE IN SAID RESISTOR, A SECOND MEANS SUPPORTING SAID CUTTER MEANS FORMOVEMENT TO THE PITCH ANGLE OF SAID HELICAL GROOVE, AND A MEANSOPERATIVELY CONNECTED WITH BOTH SAID FIRST AND SECOND MEANS FORESTABLISHING THE RATE OF MOVEMENT OF SAID CUTTER MEANS AS WELL AS THEANGLE OF SAID CUTTER MEANS.